It is known to use truck mixers to transport concrete from a production plant to the building site where the concrete is used.
Both during the loading step in the production plant and during the transport step toward the site, the concrete must be kept malleable, and therefore the rotating drum, which contains the concrete, must be kept in constant rotation to prevent the concrete from drying or hardening.
Moreover, upon arrival at the site, the truck mixer sometimes has to wait its turn to unload. During this step too, the rotating drum must be kept in constant rotation.
Before the unloading step, the concrete undergoes a homogenization step in which the drum of the truck mixer is made to rotate at its maximum rotation speed.
During the unloading step of the concrete the drum is made to rotate in a direction opposite the mixing direction.
In known truck mixers, the rotation of the rotating drum occurs normally using a hydraulic motor, which is moved by a group of pumps commanded by a heat engine which is usually a diesel engine. The heat engine can be the one that moves the vehicle or an auxiliary engine independent from that of the vehicle which is mounted on it.
One disadvantage of known truck mixers is that, in order to command the hydraulic motor associated with the rotating drum, the heat engine must be kept always in motion, during both the loading step and the unloading step of the concrete, at least until the unloading step is finished, with consequent emissions of exhaust gases which are harmful both for the health and the environment.
From documents JP-A-2003/226192, JP-A-2003/301802, and from document DE-U-20 2009 001416 a solution is known in which the rotating drum of the truck mixer is driven by means of an electric motor.
In particular, document JP-A-2003/226192 describes a truck mixer provided with a rotating drum connected directly, by means of reduction members, to the electric motor. The electric motor is fed, depending on the functioning conditions, either by an electric energy generator driven directly by the heat engine of the truck mixer, or by electric energy accumulation batteries. The selection of the electric feed to the electric motor by the generator or the batteries is done by a switch. Stabilization devices are also provided, to stabilize the electric energy supplied by the electric generator and speed adjustment devices.
This solution is not very efficient, it has a reduced operating flexibility and low electric yield, with a consequent reduction in functioning autonomy.
One purpose of the present invention is to obtain a truck mixer whose drum is made to rotate exclusively by means of electric means without requiring a hydraulic type application as provided in document JP-A-2003/301802 for example.
Another purpose of the present invention is to obtain a truck mixer provided with electric means to actuate the drum which are efficient, flexible and which allow to obtain a higher functioning autonomy.
Another purpose of the present invention is to obtain a truck mixer provided with a device able to make the rotating drum of the cement mixer rotate without needing to keep the heat engine functioning when the vehicle is stopped.
Another purpose of the present invention is to achieve a reduction in fuel consumption, for example diesel oil, and a reduction of the corresponding emissions, for example carbon dioxide and particulate, thus avoiding problems of cost and environmental pollution.
Another purpose is to achieve a reduction in noise and to safeguard the health of the people who are in the vicinity of the truck mixer, including the operators at the building site where the truck mixer is.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.